Heretofore, a number of systems have been developed to non-mechanically steer an airborne antenna of a communication system. These previous systems have been less than satisfactory because of degradation of antenna performance parameters such as: gain, axial ratio, beam width, and sidelobe levels, to illustrate a few examples. Such parameters were noted to be degraded as a function of the steering angle of such non-mechanically steered systems. Further, early non-mechanical steered systems had limited coverage of the total field of view from a given position.
In accordance with the present invention there is provided a system for mechanically steering an airborne antenna that provides for more than hemispherical coverage as the antenna is differentially positioned about non-orthogonal azimuth and elevational axes. Mechanically steering the antenna provides the advantage of minimizing or eliminating the degradation of the important antenna figures of merit.
The antenna system of the present invention meets the technical requirements of satellite networks with which the antenna may interface. For example, the antenna steered by the system of the present invention finds utility in communication with a satellite system for air traffic control, passenger telephone and telex services, airline communications, and navigational communications, all over either secure or clear transmission links.
Typically the antenna of the present invention which may be positioned by the system of the present invention comprises a radiating helical element that is designed to maximize antenna gain and minimize axial ratio. In one embodiment of the invention, the element itself is surrounded by a metal cone in an effort to decrease the beam width of the helical element with the resulting advantage of increasing the gain of the antenna. Such a metal cone, however, is not a requirement for operation of the helical antenna of the present invention. In a conventional communication system, the helical antenna element interfaces to a diplexer, a low noise amplifier, and a high power amplifier.
Although not limited thereto, the steering system of the present invention finds application for mounting an antenna on the vertical stabilizer of a Boeing 747 type aircraft. Also, the steering system finds utility for mounting an antenna on the fuselage of many presently operating aircraft. In all applications, a radome protects the antenna and the positioning system from the airborne environment, and provides an installation with a desired aerodynamic shape to minimize drag.